1. Field of Invention
Invention relates to the field of process metrology in semiconductor manufacturing and more particularly to the pattern process characterization in advanced lithography and etch technology.
2. Description of Related Art
The semiconductor industry is faced with the increased need to make features with smaller critical dimensions. To address this need, lithography processes had to be extended with techniques such as optical proximity correction, phase shifting, scattering bars, and off-axis illumination, allowing the industry to extend the life of deep ultraviolet lithography beyond the sub-wavelength barrier.
In advanced lithography, the effect of optical proximity is pronounced and very significant. Optical proximity effect manifests itself in the features where the line ends become short or long depending on whether it is positive or negative resist is used, line widths increase or decrease based on local density patterns, corners are rounded instead of being at right angles. Some of the factors causing the optical proximity effect are optical factors such as the interference of light beams transmitted through adjacent patterns, variation in the resist processes influenced by the quality of the resist, bake temperature and length of wafer baking, and resist development time, reflection from the substrate, and irregularities of the substrate. Optical proximity correction (OPC) is the set of corrective measures used in lithography to compensate for the presence or absence of adjacent features. For example, for structure lines that become shorter and rounded, OPC measures may include lengthening the line and or using enlargements at the ends such as hammerheads and serifs. Alternatively, different parts of the pattern may be widened or narrowed to compensate for the projected optical proximity effect.
Micro loading effect is caused by the etching rate varying in a chip or wafer depending on the density of the pattern components. An area or segment of a pattern may be over-etched or under-etched based on number and type of nearby pattern components. Dummy patterns are used to compensate for the micro loading effect.
Phase shift mask is an advanced lithography process of shifting the intensity profile of the light for the purpose of controlling the focus settings so as to create an asymmetrical displacement of the photoresist pattern. The mask may employ multiple degrees of phase shifting across the mask depending on the pattern to be formed. The type of resist, the difference in the multiple phases of the light on each side of the light shielding pattern, the focus and length of light exposure may all be controlled collectively to provide the desired patterning results.
Test patterns are used to characterize optical proximity, micro loading, and other process effects. For example, the five-finger-bar pattern is commonly used to determine the process effect and corrective effect of a pattern design. Whether it is the use of OPC measures, dummy patterns to compensate for the micro loading effect, or the use of phase shift masks, there is a need for metrology methods to get a more two-dimensional or three-dimensional profile of the grating features of the test pattern in order to evaluate the effect of these corrective measures. Although there are numerous non-destructive techniques for linewidth measurements, such as the scanning electron microscope (SEM) and optical microscope, none of these methods can provide complete profile information. Cross-sectional profile metrology tools, such as the atomic force microscope (AFM) and the transmission electron microscope that provide profile information are either too slow and or destructive; thus, these metrology devices are not implemented for in line/in situ applications.
Two optical metrology equipment setups may be used in optical profile metrology to measure test patterns in a non-destructive manner: those of spectroscopic reflectometry and spectroscopic ellipsometry. In spectroscopic reflectometry, the reflected light intensities are measured in a broadband wavelength range. In most setups, nonpolarized light is used at normal incidence. The biggest advantage of spectroscopic reflectometry is its simplicity and low cost.
In reflectometry, only light intensities are measured. R=|r|2 is the relation between the reflectance R and the complex reflection coefficient r.
In spectroscopic ellipsometry, the component waves of the incident light, which are linearly polarized with the electric field vibrating parallel (p or TM) or perpendicular (s or TE) to the plane of incidence, behave differently upon reflection. The component waves experience different amplitude attenuations and different absolute phase shifts upon reflection; hence, the state of polarization is changed. Ellipsometry refers to the measurement of the state of polarization before and after reflection for the purpose of studying the properties of the reflecting boundary. The measurement is usually expressed as:   ρ  =            tan      ⁢              xe2x80x83            ⁢      Ψ      ⁢              xe2x80x83            ⁢      exp      ⁢              xe2x80x83            ⁢              (                  j          ⁢                      xe2x80x83                    ⁢          Δ                )              =                  r        p                    r        s            
where rp and rs are the complex reflection coefficient for TM and TE waves.
Ellipsometry derives its sensitivity from the fact that the polarization-altering properties of the reflecting boundary are modified significantly even when ultra-thin films are present. Consequently, ellipsometry has become a major means of characterizing thin films.
The advantage of ellipsometry over reflectometry is its accuracy. First, ellipsometry measures the polarization state of light by looking at the ratio of values rather than the absolute intensity of the reflected light. Second, ellipsometry can gather the phase information in addition to reflectivity information. Phase information provides more sensitivity to the thin-film variation. Regardless of the technique used, there is a need for a non-destructive, high throughput accurate profile extraction tool for test patterns that can implemented real-time in a fabrication line.
Invention resides in a method and system for an accurate profile characterization of test patterns that can be implemented for real-time use in a fabrication line.
One embodiment of the present invention is a non-destructive method for acquiring the profile data of test pattern lines in a macro-grating test pattern, the method comprising fabricating a set of test patterns in a wafer, obtaining spectrum data from the set of test patterns using an optical metrology device, and accessing the profile data associated with the closest matching calculated spectrum data in a macro-grating profile library. The set of test patterns in the macro-grating test pattern comprises a number of clustered test pattern lines and a number of isolated test pattern lines. The set of test patterns in the wafer may be designed to evaluate the optical proximity, micro-loading, and other process effects.
In one embodiment, the optical metrology device comprises an ellipsometer or a reflectometer. Some applications of the present invention include obtaining of the spectrum data and accessing the profile data in real-time at the fabrication site. The profile data comprises detailed geometric information of each sub-feature of the macro-grating, such as width of test pattern lines, distances between test pattern lines, and or height of the features in the macro-grating test pattern.
The present invention also includes a system for acquiring the profile data of test pattern lines of a macro-grating test pattern comprising a macro-grating profile library generator for generating a macro-grating profile library comprising profile data and calculated spectrum data, an optical metrology device for measuring spectrum data from the macro-grating test pattern, and a profiler application server. The profiler application server compares the calculated spectrum data to the measured spectrum data from the optical metrology device, obtains the closest matching calculated spectrum data in a macro-grating profile library instance compared to the measured spectrum data, and accesses the associated profile data in the macro-grating profile library instance.